Ultrasonic imaging of nonlinear scatterers buried in a medium

Abstract

An ultrasonic technique for imaging nonlinear scatterers, such as cracks, buried in a medium has been recently proposed. The method called amplitude modulation consists of a sequence of three acquisitions for each line of the image has been implemented on conventional phased array ultrasonic devices. The first acquisition is obtained by transmitting with all elements of the phased array while the second and third acquisitions are obtained by transmitting with odd elements only and even elements only, respectively. An image revealing nonlinear scattering from the medium is reconstructed line by line by subtracting the responses measured with second and third acquisitions (odd elements and even elements) from the response obtained with all elements transmitting. The proof of concept was performed on a unique sample which has shown that amplitude modulation has a higher detection specificity and a better contrast of the crack than the conventional ultrasound image. The goal of this study is to gain a better knowledge of the capabilities of the amplitude modulation method by determining its sensitivity and robustness compared to the conventional imaging for several stainless steel samples with different grain sizes as well as different crack sizes and orientations.